The present invention relates to a magnetic recording medium, particularly a rotatable magnetic recording medium, such as a thin film magnetic disk and a lubricant topcoat for contact with a cooperating magnetic transducer head. The invention has particular applicability to a textured magnetic recording medium comprising a lubricant topcoat that adheres to the magnetic recording medium.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a xe2x80x9chead crash.xe2x80x9d Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as xe2x80x9ctexturing.xe2x80x9d Conventional texturing techniques involve mechanical polishing or laser texturing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers. The surface of an underlayer can also be textured, and the texture substantially replicated in subsequently deposited layers.
A typical longitudinal recording medium is depicted in FIG. 1 and comprises a substrate 10, typically an aluminum (Al)-alloy, such as an aluminum-magnesium (Alxe2x80x94Mg)-alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, glass-ceramic materials and graphite. Substrate 10 typically contains sequentially deposited on each side thereof a chromium (Cr) or Cr-alloy underlayer 11, 11xe2x80x2, a cobalt (Co)-base alloy magnetic layer 12, 12xe2x80x2, a protective overcoat 13, 13xe2x80x2, and a lubricant topcoat 14, 14xe2x80x2. Cr underlayer 11, 11xe2x80x2 can be applied as a composite comprising a plurality of sub-underlayers 11A, 11Axe2x80x2.
The protective overcoat desirably possesses high durability, density and hardness to protect the underlying magnetic layer providing wear resistance and encouraging durability of the magnetic recording medium arrangement. Typically, a thin film of zirconium oxide, silicon oxide or carbon is used as a protective overcoat.
Chromium underlayer 11, 11xe2x80x2, Co-base alloy magnetic layer 12, 12xe2x80x2 and protective overcoat 13, 13xe2x80x2 are usually deposited by sputtering techniques performed in an apparatus containing sequential deposition chambers. A conventional Al-alloy substrate is provided with a NiP plating, primarily to increase the hardness of the Al substrate, serving as a suitable surface to provide a texture, which is substantially reproduced on the disk surface.
In accordance with conventional practices, a lubricant topcoat is uniformly applied over the protective overcoat to prevent wear between the disk and head interface during drive operation. Excessive wear of the protective overcoat increases friction between the head and disk, thereby causing catastrophic drive failure. Conversely, excess lubricant at the head-disk interface causes high stiction between the head and disk. If stiction is excessive, the drive cannot start and, likewise, catastrophic failure occurs.
The drive towards ever increasing recording density, and faster data transfer rates and the resulting smoother disk surfaces and lower flying heights, has served as an impetus for the development of new lubricants to serve as a lubricating topcoat overlying the protective overcoat. Such lubricants must perform a variety of different purposes requiring diverse characteristics and attributes. For example, the lubricant forming the topcoat is preferably chemically inert, possesses a low vapor pressure, low surface tension, high thermal stability, stability under high shear stress and good boundary lubrication properties. Moreover, it is critical that the lubricant tightly adheres to the underlying surface over the lifetime of the magnetic recording media.
Several classes of lubricants may satisfy many of the desired properties. Among the many lubricants available, liquid perfluoropolyethers (PFPE) are the most utilized for forming topcoat lubricants on magnetic recording media. PFPE""s have been reported for use as lubricating magnetic media in, for example, U.S. Pat. No. 3,778,308. However, there continues to be a need to improve the adhesion of lubricants to the magnetic media while maintaining the desired tribological properties.
It is believed that to achieve adhesion of the lubricant to the magnetic media requires the inclusion of polar and reactive functional groups, particularly on the end of the lubricating compound. In this regard, several patents have disclosed the use of functionalized PFPE for improved bonding of the lubricant to the magnetic media. For example, U.S. Pat. No. 4,069,360 discloses magnetic storage means containing a lubricant which consists of an oil group, such as silicon oil, and a reactive surface coupling end group, such as a chlorosilane or a disilazane. U.S. Pat. No. 4,120,995 discloses a process for bonding a polymeric coating to a metal or oxide surface including treating the surface with a polymer having a reactive siloxane, halosilane or cyanosilane end group. U.S. Pat. No. 4,268,556 discloses lubricating magnetic recording disks with fluorinated telechelic polyether polymers containing highly polar end-groups. U.S. Pat. No. 4,696,845 discloses a lubricant layer for a magnetic surface, having functional groups at various locations on the lubricant molecule and U.S. Pat. No. 5,820,964 discloses a lubricant film comprising an adhesion enhancing layer and a lubricating agent which, together, form a salt complex on a magnetic disk.
Other functional perfluoropolyether compounds are known. U.S. Pat. No. 3,810,874 discloses the preparation of polyfunctional-terminated poly(perfluoroalkylene oxide) materials. U.S. Pat. No. 4,085,137 discloses polyfunctional poly(perfluoroalkylene oxide) compounds containing polymerizable functional end groups. While lubricants including polar or functional end-groups have improved adhesion under certain conditions, many of these functional lubricants compromise the stability and durability of the lubricant topcoat over time.
In view of the criticality of the lubricant topcoat in magnetic recording media, there is a continuing need for improved uniform bonding of the lubricant topcoat to the magnetic recording medium, particularly to a protective overcoat while maintaining or improving the diverse characteristics and attributes desirable in lubricant topcoats. There is also a need for improved lubricants for use as topcoats in the manufacture of magnetic recording media capable of achieving a high bonding to the underlying protective overcoat.
An advantage of the present invention is a magnetic recording medium comprising a uniform lubricant topcoat substantially bonded to the magnetic recording medium.
Another advantage of the present invention is a method of manufacturing a magnetic recording medium comprising forming a uniform lubricant topcoat that tightly adheres to the magnetic recording medium.
A further advantage of the present invention is a lubricant useful as a lubricant topcoat on a magnetic recording medium capable of tightly adhering to a magnetic recording medium.
Additional advantages and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a magnetic recording medium comprising a lubricant topcoat, wherein the lubricant topcoat comprises a fluoropolyether having a non-functional end-group. The lubricant topcoat of the present invention comprises a fluoropolyether having a non-functional silane end group, which advantageously achieves no less than 70% bonding to the magnetic recording medium. The inventive lubricants additionally can achieve the formation of highly uniform topcoats, as evidenced by measured water contact angles of in excess of about 100 degrees.
Embodiments of the present invention include a fluoropolyether having the following formula: 
wherein Z is a fluoropolyether; X is a linker group, if present; R1, R2, and R3 are independently alkyl or aryl; R4 is a substituted or unsubstituted alkylene or arylene; and q is 1 to 4.
Another aspect of the present invention is a method of manufacturing a magnetic recording medium. The method comprises: forming a magnetic layer on a non-magnetic substrate; and forming a lubricant topcoat on the magnetic layer, wherein the lubricant topcoat comprises a fluoropolyether having a non-functional silane end group. Embodiments include means for lubricating the magnetic layer, wherein the lubricating means comprises a fluoropolyether having a nonfunctional silane end group and bonding about 70% or more of the fluoropolyether to the magnetic layer. The method further comprises: forming an underlayer on the non-magnetic substrate; forming the magnetic layer on the underlayer, forming a protective overcoat on the magnetic layer; and forming the lubricant topcoat on the protective overcoat. In an embodiment of the present invention, the protective overcoat comprises a carbon containing layer and about 90% or more of the fluoropolyether is bound to the carbon layer.
Additional advantages of the present invention will become readily apparent to those having ordinary skill in the art from the following detailed description, wherein the embodiments of the invention are described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.